The invention relates to a steering gear for a power-assisted steering system of a motor vehicle, and in particular a fixed bearing for such a steering gear.
In most motor vehicles, power-assisted steering systems are installed which generate a supporting torque during steering and as a result reduce the steering torque which has to be applied to the steering column by the driver.
The known power-assisted steering systems are based on a steering gear which converts the driving power of a hydraulic or electric drive and transmits it to the steering column. Such steering gears are generally embodied in the form of a screw rolling gear, and in particular as a helical gear or worm gear, i.e. the latter comprise a gear wheel which is connected directly or indirectly to the steering rod, and a pinion which meshes therewith and is driven by the drive via a pinion shaft.
Gearing play which is formed owing to component tolerances, different widths of thermal expansion of the gear elements and owing to wear has proven problematic in such steering gears. In particular, in the case of what is referred to as alternating steering, that is to say, in the case of directly successive steering with alternating steering lock, such gearing play generates undesired noises which result from alternating abutment to opposite flanks of the teeth of pinion and gear wheel.
It is known for said gearing play to be eliminated by virtue of the pinion shaft being mounted so as to be pivotable about an axis running perpendicular to the longitudinal axis of the pinion shaft and at a distance to the toothing engagement of the pinion and gear wheel, and being pressed against the gear wheel by means of one or more spring elements. Here, the pivoting capability of the pinion shaft is integrated into one of the two bearing arrangements over which the pinion shaft is mounted at its ends. This bearing arrangement is referred to as “fixed bearing”. The bearing arrangement in the region of the other end is then implemented with play (so-called “floating bearing”) in order to permit the deflection caused by the pivoting movement. The fixed bearing is generally provided at the drive side, while the floating bearing is provided at the free end of the pinion shaft. The spring element or elements for pressing the pinion against the gear wheel are generally integrated into the floating bearing.
Such a steering gear is known, for example, from WO 2011/073039 A1. In said document there is a provision for the roller bearing which receives the pinion shaft in the region of the fixed bearing to be mounted on the outside in a pivoting bushing. The pivoting bushing comprises a bearing bushing which receives the roller bearing largely free of play, and an outer ring which is secured largely free of play in a drilled hole in a housing of the steering gear, wherein the outer ring and the bearing bushing are connected via a plurality of webs which are twisted during rotation of the outer ring with respect to the bearing bushing. The entire pivoting bushing is constructed in one piece in the form of a sheet-metal component.
A configuration of a steering gear which is similar to WO 2011/073039 A1 is described in the German patent application 10 2012 103 146.0 which has not been published to date. In said document, the pivoting ring is, however, embodied as a separate component. In this concept, the pivoting ring comprises an inner ring and an outer ring which is connected to the inner ring via two torsion webs. The outer ring serves to support the fixed bearing in the housing of the steering gear, while the inner ring is clamped between the roller bearing and a radially inwardly bent-over end of the bearing bushing. In order to be able to introduce the inner ring of the pivoting ring into the bearing bushing, the bearing bushing is provided at the corresponding longitudinal end with two longitudinal slots which serve to receive the torsion webs.
A disadvantage with this fixed bearing is the relatively complex manufacture (owing to the longitudinal slots which have to be put in place) and the relatively complicated mounting (owing to the necessary precise orientation of the bearing bushing relative to the pivoting ring). In addition, the bearing bushing is structurally weakened by the longitudinal slots, which can lead to undesired mobility of the roller bearing and therefore of the bearing arrangement of the pinion shaft.